If I turn my laptop on an angel that is not transparent.Anyways, if you have GIMP just go to layer, transparency, add alpha channel, select magic wand (The little wand icon), and click the part you want transparent, then click the delete key.

You can use paint.NET, though it doesn't always work. Take out your picture (with a plain background, or it won't work.) and click on the magic wand. Select the background and the press the delete key.